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A myth has grown up that people who enter an election voting booth do just as newspapers tell them in the days beforehand. Politicians are particularly prone to believing this nonsense.

Even some editors — though denying publicly that their advice makes any difference — like to think it may be crucial to the outcome.

This cause-and-effect analysis of press power has been to the fore in recent weeks during the build-up to yesterday’s US presidential election.

American newspapers, often with great pomposity, gave their readers the benefit of their editorial boards’ considered views on whether they should vote for Barack Obama or Mitt Romney. Though most sensible media commentators in the States believe such endorsements make little, or any, difference, it hasn’t curbed the habit. For some reason, publishers and editors like to boast about their preference.

Journalists would do well to consider the reality. In 2008, for example, several leading metropolitan papers in states which eventually voted for Obama had endorsed the Republican contender, John McCain.

This time around, Romney enjoyed 35 newspaper endorsements, 10 more than McCain received. Obama picked up 41, but that was way down on 2008 when 65 papers — with a total circulation of more than 16 million — gave him their backing.

Naturally enough, the greatest attention was paid by the candidates’ teams to the endorsements of the major papers in the swing states. Most of the Florida papers, for example, opted for Romney, though the largest of them, the Miami Herald, backed Obama.

In the key state of Ohio, three papers endorsed Romney and two, the Cleveland Plain Dealer and the Toledo Blade, stuck with Obama. As for Wisconsin, where two papers are dominant, the State Journal (based in Madison) and the Journal Sentinel (Milwaukee), the former switched from Obama to favour Romney and the latter, having backed Obama in 2008, refused to endorse either candidate this year.

I always find it surprising that American papers, which pride themselves on impartiality, feel it necessary for one day every four years to nail their political colours to the mast. By contrast, British papers have traditionally been unashamedly, even proudly, partisan every day of every year. But their politics is tempered by their desire to project their independence.

For instance, the Conservative-supporting part of the national press has not been inhibited in the least from being sharply critical of the Tory party in the post-Thatcher era and certainly not since the election of a coalition Government.

What they are saying and doing now, however, is much more important than what they urge their readers to do in the final weeks of an election campaign. When the Daily Telegraph runs headlines and leading articles just before polling day that say “Vote Tory” they will know that their most influential pro-Tory spadework was done in the previous five years.

When the Sun ditched Gordon Brown in favour of David Cameron in September 2009, it may have been a shock to Brown, but the paper’s readers had surely picked up its editorial disenchantment with Labour months before.

Anyway, by switching sides eight months before the general election, it gave the paper time to reinforce its pro-Conservative — and virulently anti-Labour message — every day.

But the key point to keep in mind is that it didn’t work. Despite the might of the Sun, the Daily Mail, the Daily Telegraph, The Times and the Daily Express all endorsing the Tories, the party was unable to secure an outright election victory.

The people did not do as they were told. Some might have been swayed by what they were reading in their daily newspapers about Labour’s (and Brown’s) failures but there were too few of them to give Cameron a working parliamentary majority.

Nor can we rely on “impartial” broadcasters to provide a clear view ahead of an electoral result; TV and radio correspondents are slaves to polls and to that other extraordinarily facile routine of vox pop interviews.

What’s the point of that exercise? Throughout the presidential election campaign, I watched with increasing annoyance as reporters stuck a microphone into a shopper’s face and asked which way they would vote and why.

To achieve “balance”, they ensured that an equal number of people spoke up for each candidate.

So what did that tell us? Well, it most certainly didn’t reveal that Obama would be re-elected.

Roy Greenslade is Professor of Journalism, City University London, and writes a blog for the Guardian